After looking at pictures of Urie S15s, it struck me that I was using the wrong motion support bracket. I'd originally folded up the right one, then put it back in the box as it didn't look like the one in the chassis instructions - there were two brackets supplied. I'm guessing that the chassis instructions are generic for S15s, and it's left to you to figure out which bits are specific for the Urie variants. In any case, the correct bracket looks a lot better, although it needed a massive amount of brass removed before it sat nicely on the frame notches.

Once that was established, I then carried on with the valve gear. I first assembled the radius rod, then the lifting link that tucks up through the bracket and (in reality) connects with the reversing lever running from the cab. I then assembled the fly crank and associated rod onto the expansion link. The next job was to attach the expansion link to the motion bracket, which is achieved by fixing an M1 screw from the outside, retaining the expansion link and the end of the radius rod. Everything fitted, but the bolt has to have a tiny M1 nut screwed onto it from inside the bracket, which was the devil's very own job! I used tweezers to fiddle the nut onto the bolt, patiently trying again and again until it found the thread instead of falling off into the stygian gloom of my work bench.

All that remained was to attach the fly crank to the main driving wheel, applying the appropriate "lead" relative to the coupling rods. For the time being, I've retained it with a drop of cyano but I've still to solder the final crankpin washer into place and I'm fairly sure that will burn off the cyano! Initial testing was not encouraging, but after some dis-assembly and tweaking it all came good, albeit with a slight tight spot. I then realised (after the above photo was taken) that the motion bracket was set a little too far ahead, the mounting for it being a slot rather than a hole as in the first bracket. I loosened the bracket, eased it back as far as it would go, and then reassembled. Touch wood, but that seems to have eliminated the tightness, with the loco now running as smoothly as it was before I added the valve gear. Presumably the bracket being too far forward was asking too much travel of the fly crank rod and expansion link.

It's not quite time to break out the bubbly as I still have to do the other side! I can't wait to get to that M1 nut and bolt again! However with a week of travel ahead of me, that fun will have to wait until I get back.